Study On The Preparation And Properties Of LZAS Glass-ceramics CBN Composites

cBN has been widely used to process the iron and ferrous materials due to its highhardness, strength, wear resistance and so on. The glass–ceramics cBN composites wereburied in graphite powders. The Li2O–ZnO–Al2O3–SiO2(LZAS) glass–ceramics were chosenas the bond of cBN. Analytical pure reagents were used as raw materials to prepareglass–ceramic powders. The major crystalline phase was β–spodumene, and the secondcrystalline phase was Li8Zn10Si7O28. K2O and Na2O was chosen to modify and optimize theglass–ceramic properties, and the effects of glass–ceramics without K2O and Na2O and withdifferent molar ratio of K and Na on the properties of bond were studied. Moreover, thecomposition and content, firing temperature and holding time on the properties ofglass–ceramics cBN composites were researched. Finally, the influence of particle sizegradation of cBN on the porosity, volume density and bending strength of glass–ceramic cBNcomposite was also studied.The main results were shown as follows:(1) K2O and Na2O could also reduce the glass transition temperature, restrain the crystalformation of virgilite, and promote the crystal formation of Li8Zn10Si7O28and the transformfrom virgilite to β–spodumene. When the molar ratio of K to Na was1.5, the bending strengthof the glass–ceramic bond achieved maximum which was84.6MPa. At the same time, thesoftening temperature was940℃, the fluidity was136%, and the thermal expansioncoefficient was4.53×10-6/℃which was near to the cBN.(2) The composition and content of glass–ceramics were the most significant factors. Themore content of glass–ceramics and the higher molar ratio of K and Na, the higher bendingstrength and the better density of cBN composites. The porosity decreased59.82%and thebending strength increased37.97%when the content of glass–ceramics increased from10%to40%. Compared to the composite without K2O and Na2O, when the ratio of K to Na was1.5, the porosity decreased20.87%and the bending strength increased29.26%. And theoptimal comprehensive properties of the cBN composite were achieved. The porosity of thecomposite was13.9%, the relative density was89.48%, the bending strength was96.3MPa,and the vickers hardness was420MPa.(3) The particle size gradation of cBN could enhance the properties of glass–ceramic cBN composites. When the particle size distribution of cBN was7:1:2and the content ofglass–ceramic bond was20wt%, the glass–ceramic cBN composites achieved the optimumproperties. The porosity reached the minimum which was8.55%, the relative density achievedthe best which was91.89%, the bending strength achieved the optimum which was167.6MPa, and the vickers hardness was874MPa. The bending strength of cBN composites was74%higher than that with uniform size of cBN.